The objective of this project is to expand understanding of health risks from polluted ambient air, by identifying specific pollutants and meteorological conditions which cause specific physiological and clinical effects. The aim is to document short-term health-related responses in human volunteers breathing atmospheres containing "acid fog" under controlled conditions. The exposure atmospheres will closely resemble Southern California fogs, and will also be relevant to Eastern fogs of the type associated with past air pollution disasters. The overall plan involves coordination with on-going and planned atmospheric chemistry and animal toxicology studies. Initially, healty volunteers will be exposed in a chamber to fog containing sulfuric and/or nitric acids in otherwise pure air, under conditions simulating "worst-case" ambient exposures as determined in the atmospheric studies. If few or no effects are found, volunters with chronic respiratory disturbances will then be studied. In later years, potentially irritating substances identified in the atmospheric and toxicologic studies may be added to the controlled-exposure atmospheres. A second, concurrent task will employ a unique movable human exposure/air monitoring laboratory to expose volunteers to ambient acid fogs during actual ambient fog conditions. The frequency and geograhical location of ambient fog episodes will be carefully investigated during the initial year of the program to assess the opportunities for a successful ambient acid fog field exposure program.